Soft, extended wear contact lenses are currently in use which incorporate gas permeable plastics as structural materials and holes and edge treatment to supply the cornea with the oxygen required to prevent changes to the endothelial cells and edema or cornea swelling. These various devices enhance the flow of lachrymal fluids under the lens to supply the cornea with the required oxygen. As the permeability of the lens material is reduced and the bleed apertures closed due to contamination by sloughed-off epithelial cells and metabolic wastes, evaporation of the fluids on the cornea surface is reduced and the cornea is warmed by the blood supply. This is irritating and dangerous because the temperature of the cornea must remain at a level relatively lower than body temperature or its metabolic process will accelerate and contamination of the lens will speed up until it rapidly reaches a point where it constitutes a significant health threat.
Numerous attempts have been made to solve the above problems but the end results of these approaches is that the wear duration of the lens is slightly extended but ultimate contamination unbeknown to the wearer still occurs and a health threat is presented. For instance, B. Meyer in U.S. Pat. No. 4,621,912 on "Foraminated Optical Contact Lens" provides a plurality of micropore passageways through the lens surfaces. When this lens is first installed, it performs the needed function of allowing waste materials to be bled off from the underside of the lens but due to the extremely small size of the holes, they quickly clog and the aforesaid contamination and heat buildup problems begin their rapid chain reaction.
D. Riddle, U.S. Pat. No. 2,393,266 on "Contact Lens" is a relatively early example to solve contaminant buildup on the underside of the contact lens. In this approach, radial channels are provided on the cornea side of the lens and terminate in holes passing completely through the lens which allows the channeled waste material to exit the under surface. This system, as in Meyer above, quickly clogs and the contamination spiral rapidly accelerates.
Another early approach which is the concept of providing a plurality of cuts in the peripheral portion of the lens which are in the form of short arcs such as taught by Becker in U.S. Pat. No. 3,228,741 on "Corneal Contact Lens Fabricated From Transparent Silicone Rubber". Becker suggests arc shaped channels having a radius which originates at the center of the lens but this approach has proved unsuccessful because material buildup under the lens quickly reaches a point where irritation of the eye begins.
Lenses have been made with small holes drilled through the lens (fenestration), in an effort to overcome this problem. Lens material is removed to produce the hole. If the holes are large, they will be seen by the wearer and by others, and if they are small enough not to be seen, they become clogged with body secretions and they become useless. An example of this technology may be found in C. Neefe, U.S. Pat. No. 4,401,371, at Column 1, Lines 28-32.
Clogging of small "fenestration" holes in the prior art lenses such as Neefe discussed above or C. Wichterle, U.S. Pat. No. 4,666,267 is due to the fact that the hole walls are rigid and they do not flex with eye blinking to thereby flex the hole walls and dislodge the deposits as they accumulate during normal usage of the lens.
In addition to the above-mentioned problems, there is the problem of compliance of a contact lens wearer with the recommendations of lens manufacturers and ophthalmologists, regarding regular changing/discarding and/or properly cleaning a lens. Unless these recommendations are faithfully followed, particularly with disposable and extended wear contact lenses, the lenses are rendered hygienically unsuitable for further wear and are dangerous to the health of the wearer. Moreover, the recommendations for proper maintenance/change of the lenses represent an average that does not take into account the variations of eye physiology among individuals environmental conditions (such as dustiness). For one person discarding/cleaning his/her lenses every two weeks may be adequate, whereas for another person, or for the same person in a different environment, this time interval may be shortened to a few days.
A need therefore exists for an indicator for soft contact lenses which provides a signal of progressive intensity to a contact lens wearer of contaminate buildup. This must not interfere with normal vision, and must be detectable only by the lens wearer, signifying to the lens wearer that it is time to change, dispose and/or properly clean the lenses.
Additionally, the indicator, should not alter the soft lens composition or necessitate the introduction of new substances into the lens, and it must be applicable to all soft contact lenses.